mongodb Mongo group and push：推送所有字段
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Mongo group and push: pushing all fields
提问by Pelit Mamani
Is there an easy way to "$push" all fields of a document? For example:
有没有一种简单的方法来“$push”文档的所有字段？例如：
Say I have a Mongo collection of books:
假设我有一本 Mongo 书集：
{author: "tolstoy", title:"war & peace", price:100, pages:800}
{author: "tolstoy", title:"Ivan Ilyich", price:50, pages:100}
I'd like to group them by author - for each author, list his entirebook objects:
我想按作者对它们进行分组 - 对于每个作者，列出他的整本书对象：
{ author: "tolstoy",
books: [
{author: "tolstoy", title:"war & peace", price:100, pages:800}
{author: "tolstoy", title:"Ivan Ilyich", price:50, pages:100}
]
}
I can achieve this by explicitly pushing all fields:
我可以通过显式推送所有字段来实现这一点：
{$group: {
_id: "$author",
books:{$push: {author:"$author", title:"$title", price:"$price", pages:"$pages"}},
}}
But is there any shortcut, something in the lines of:
但是是否有任何捷径，例如：
// Fictional syntax...
{$group: {
_id: "$author",
books:{$push: "$.*"},
}}
回答by Jurjen Ladenius
You can use $$ROOT
您可以使用 $$ROOT
{ $group : {
_id : "$author",
books: { $push : "$$ROOT" }
}}
Found here: how to use mongodb aggregate and retrieve entire documents
在这里找到：如何使用 mongodb 聚合并检索整个文档
回答by Neil Lunn
Actually you cant achieve what you are saying at all, you need $unwind
实际上你根本无法实现你所说的，你需要$unwind
db.collection.aggregate([
{$unwind: "$books"},
{$group: {
_id: "$author",
books:{$push: {
author:"$books.author",
title:"$books.title",
price:"$books.price",
pages:"$books.pages"
}},
}}
])
That is how you deal with arrays in aggregation.
这就是你在聚合中处理数组的方式。
And what you are looking for to shortcut typing all of the fields does not exist, yet.
并且您正在寻找的快捷方式键入所有字段尚不存在。
But specifically because of what you have to do then you could notdo that anyway as you are in a way, reshaping the document.
但特别是因为你必须做的事情，你无论如何都不能这样做，因为在某种程度上，重塑了文档。
回答by Ivan.Srb
If problem is that you don't want to explicitly write all fields (if your document have many fields and you need all of them in result), you could also try to do it with Map-Reduce:
如果问题是您不想显式写入所有字段（如果您的文档有很多字段并且您需要所有这些字段），您也可以尝试使用 Map-Reduce 来完成：
db.books.mapReduce(
function () { emit(this.author, this); },
function (key, values) { return { books: values }; },
{
out: { inline: 1 },
finalize: function (key, reducedVal) { return reducedVal.books; }
}
)
